arXiv subjects
Publications and source records attributed to Anthony C. Crawford.
A deeply modulated, regular, continuous, oscillating current waveform is reliably and repeatably achieved during electropolishing of niobium single-cell elliptical radiofrequency cavities. Details of the technique and cavity test results are reported here. The method is applicable for cavity frequencies in the range 500 MHz to 3.9 GHz and can be extended to multicell structures.
A significant advance in magnetic field management in a fully assembled superconducting radiofrequency cryomodule has been achieved and is reported here. Demagnetization of the entire cryomodule after assembly is a crucial step toward the goal of field less than 5x10-7 Tesla. An explanation of the basic physics of demagnetization as well as experimental results are presented.
Room temperature properties and behavior of several types of cryogenic magnetic shielding materials are measured and reported here. Large changes in the effective relative permeability are observed when the materials are perturbed with a relatively small mechanical stimulation. The change in permeability is a reversible effect.
A quasi time constant for magnetic domain relaxation of Metglas 20605SA1 has been measured to be 2.6 hours. The effective relative magnetic permeability has been measured to be 57,000 after relaxation.
This note demonstrates that the cold segments of the LCLS2 linac will cryopump hydrogen for long periods of time, mitigating concerns for beam-residual gas interactions.
This study determines a useful value to use for the gap width of mechanical overlap joints in models of magnetic shielding. The average value of 0.1 mm is found to agree with measurements.
The feasibility of in-situ demagnetization of fully assembled superconducting RF cryomodules is demonstrated. Useful parametric values for demagnetization as well as measured effects on sensitive components within the cryomodule are listed and discussed. A practical arrangement for active compensation of the axial component of magnetic field is described.
This note presents measurements that support the proposition that it is feasible to demagnetize a fully assembled superconducting RF cryomodule.
This note presents measurements that support the conclusion that it is feasible to achieve magnetic field values at the level of 5 milliGauss for a cryomodule in a realistic and representative ambient magnetic field environment.
The case of axisymmetric ILC type cavities with titanium helium vessels is investigated. A first order estimate for magnetic field within the SRF current layer is presented. The induced magnetic field is found to be not more than 1.4x10-8 Tesla = 0.14 milligauss for the case of axial symmetry. Magnetic fields due to symmetry breaking effects are discussed.